在SourceForge上看到的一个Python写的表达式解析器

from __future__ import division __doc__ = r"""Parsnip: Packrat parser for attributed Parsing Expression Grammars. (well, it will be a packrat parser eventually) A non-context-free grammar just for fun. (a^n b^n c^n) >>> ncf = "\n".join(['S := &(A ![ab]) "a"* B !.', ... 'A := "a" A "b" / empty', ... 'B := "b" B "c" / empty']) >>> P = Parser(ncf) >>> P.parse("aaabbbccc") # silently succeeds >>> P.parse("aabbbccc") Traceback (most recent call last): ParseError >>> P.parse("aaabbccc") Traceback (most recent call last): ParseError >>> P.parse("aaabbbcc") Traceback (most recent call last): ParseError >>> P.parse("aaaabbbccc") Traceback (most recent call last): ParseError >>> P.parse("aaabbbbccc") Traceback (most recent call last): ParseError >>> P.parse("aaabbbcccc") Traceback (most recent call last): ParseError >>> P.parse("aaaabbbcc") Traceback (most recent call last): ParseError The same grammar, attributed to count the number of repititions. >>> ncf = "\n".join(['S := &(A ![ab]) "a"* n:B !. {n}', ... 'A := "a" A "b" / empty', ... 'B := "b" n:B "c" {n+1} / empty {0}']) >>> Parser(ncf).parse("aaabbbccc") 3 """ license = """Copyright (c) 2004 William Isaac Carroll Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.""" # TODO: # report cause of match failure # memoize into a packrat parser # recognize left recursion # transform left recursion # transform repitition # prettyprint grammar rules (recreate PEG from data structure) class Pattern: def __repr__(self): return self.__class__.__name__ + "(" + self.args + ")" class Literal(Pattern): """ Match a literal string. >>> Literal("foo").match("foo", 0) (3, None) >>> Literal("foo").match("bar", 0) False >>> Literal("bar").match("foo", 0) False >>> Literal("foo").match("foobar", 0) (3, None) >>> Literal("foo").match("foobar", 1) False >>> Literal("oo").match("foobar", 1) (2, None) """ def __init__(self, lit): self.lit = lit self.args = repr(lit) def match(self, text, pos, env=None): if text.startswith(self.lit, pos): return (len(self.lit), None) else: return False class Range(Pattern): """ Match a single character from a range of characters. >>> Range("a", "c").match("b", 0) (1, None) >>> Range("c", "e").match("b", 0) False >>> Range("a", "c").match("d", 0) False >>> Range("a", "c").match("c", 0) (1, None) >>> Range("a", "c").match("a", 0) (1, None) >>> Range("a", "c").match("ca", 0) (1, None) >>> Range("a", "c").match("cd", 0) (1, None) >>> Range("a", "c").match("ca", 1) (1, None) >>> Range("a", "c").match("cd", 1) False >>> Range("a", "c").match("", 0) False """ def __init__(self, start, end): self.start = start self.end = end self.args = ", ".join([repr(start), repr(end)]) def match(self, text, pos, env=None): try: char = text[pos] except IndexError: return False if self.start <= char <= self.end: return (1, None) else: return False class AnyCharT(Range): """ Match any single character. >>> AnyChar.match("a", 0) (1, None) >>> AnyChar.match("", 0) False """ def __init__(self): Range.__init__(self, chr(0), chr(127)) def __repr__(self): return "AnyChar" AnyChar = AnyCharT() class Require(Pattern): """ Positive syntactic predicate. >>> Require(Literal("a")).match("a", 0) (0, None) >>> Require(Literal("a")).match("b", 0) False """ def __init__(self, pattern): self.pattern = pattern self.args = repr(pattern) def match(self, text, pos, env=None): if self.pattern.match(text, pos) == False: return False else: return (0, None) class Reject(Pattern): """ Negative syntactic predicate. >>> Reject(Literal("a")).match("a", 0) False >>> Reject(Literal("a")).match("b", 0) (0, None) """ def __init__(self, pattern): self.pattern = pattern self.args = repr(pattern) def match(self, text, pos, env=None): if self.pattern.match(text, pos) == False: return (0, None) else: return False class Labeled(Exception): """Not pretty, but it works.""" pass class Label(Pattern): """ Assign the value of a pattern to a variable. """ def __init__(self, name, pattern): self.name = name self.pattern = pattern self.args = ", ".join([repr(name), repr(pattern)]) def match(self, text, pos, env=None): result = self.pattern.match(text, pos, env) if result == False: return False else: count,value = result raise Labeled(self.name, count, value) class Seq(Pattern): """ Match a sequence of patterns. >>> Seq([Literal("a"), Literal("b")]).match("ab", 0) (2, None) >>> Seq([Literal("a"), Literal("c")]).match("ab", 0) False >>> Seq([Literal("a"), Literal("b")]).match("a", 0) False >>> Seq([Literal("a"), Literal("b")]).match("bab", 1) (2, None) >>> S = Seq([Literal("a"), Reject(Literal("b")), Range("b", "c")]) >>> S.match("ac", 0) (2, None) >>> S.match("ab", 0) False >>> Seq([]).match("abc", 0) (0, None) >>> Seq([Literal("a")], value="5").match("abc", 0) (1, 5) >>> Seq([Literal("a")], value="2+2").match("abc", 0) (1, 4) >>> Seq([Literal("a")], value="x", env=dict(x=5)).match("abc", 0) (1, 5) """ def __init__(self, patterns, value=None, env=None): self.patterns = patterns self.value = value self.env = env if self.env is None: self.env = {} pats = [repr(pattern) for pattern in patterns] if self.value is not None: pats += ["value=" + repr(self.value)] self.args = ", ".join(pats) def match(self, text, startpos, env=None): curpos = startpos if env is None: env = {} else: env = dict(env) for pattern in self.patterns: try: result = pattern.match(text, curpos, env) except Labeled, L: name,count,value = L.args result = (count, value) env[name] = value if result == False: return False else: count,_ = result curpos += count if self.value is None: value